This invention relates to pest controlling and more particularly to a sustained-release, long-term pest-control microcapsule which is environmentally friendly and non-toxic.
Use of microcapsules containing various active pest-control agents is well known. Several patents disclose such microcapsules, e.g., U.S. Pat. Nos. 3,429,827, 3,577,515, 4,280,833, 4,285,720, 4,417,916, 4,900,551, and 4,936,901. Interfacial polycondensation is often used as the technique to form microcapsules loaded with active pest-control agents, although techniques including complex coacervation and in situ polymerization can also be used. These and other microencapsulation techniques for preparing microcapsules have been described in various review articles. Microencapsulation, Thies, C., Kirk-Othmer Encyclopedia of Chemical Technology, 4th ed., Vol. 16, John Wiley, NY, 1995, pp 628-652. Microcapsule Processing and Technology, Kondo, A., (edited and revised by J. Wade van Valkenburg), Marcell Dekker, NY, 1979. Mikrokapseln, Sliwka, W., Ullmmanns Encyklopadie der technischen chemie, Vol. 16, Verlag Chemie, Weinhein, 1978, pp 675-682.
It is an important object of the invention to provide improved methods and means for pest controlling.
The invention features a sustained-release, long-term pest-control microcapsule which prolongs its potency adaptive to the temperature of the surrounding medium and which is environmentally friendly and nontoxic.
One aspect of this invention relates to a pest-control microcapsule which releases an active pest-control agent at a sustained rate, thereby prolonging the potency of the microcapsule. In general, a microcapsule includes a capsule core and a capsule shell. Historically, it has not been recognized that both the shell and core can provide resistant paths to the mass transfer of active pest-control agent contained in the capsule core. The pest-control microcapsule of the present invention utilizes this new concept, thereby reducing the rate of release of active ingredient distributed to the surrounding medium, thereby extending the length of performance of the capsules in the field, and reducing the cost of pest control as well as the potential for environmental pollution. Furthermore, candidate diluents natural and/or are biodegradable materials compatible with the environment.
The diluent is distributed in the core in such a manner that the active pest-control agent is effectively bound by the diluent and diffuses through the resistant paths formed by the diluent to reach the capsule shell through which it then diffuses. The diluent may form a solid-like, matrix-like or mesh-like structure inside the core and entrap the active ingredient inside such matrix and mesh. The diluent may also simply form a homogeneous solution with the active ingredient (AI) in which the AI and diluent interact (i.e., AI-diluent interaction), thereby slowing release of the AI from the capsule. Accordingly, a formulator can obtain desirable permeability or release rate of the active ingredient by manipulating several factors, such as the amount or percentage of the diluent contained in the capsule core, distribution pattern of the diluent in the core, method of entrapping the active ingredient in the diluent, and other physical properties of the diluent.
The capsule shell separates the core volume material from the surrounding medium, and is arranged to provide additional resistant paths to diffusion of the active ingredient from the capsules. Thus, permeability or release rate of the active ingredient can be manipulated by controlling several features of the shell such as pore size, length, density, tortuosity, pattern of pore distribution, and other physical properties of the material composing the shell.
A pest-control microcapsule can be composed in such a way that the permeability or release rate of the active ingredient depends upon the physical and/or chemical properties and melting point of the diluent and the temperature of the surrounding medium. Lipids such as oils, waxes, fats cholesterol are used as diluents and incorporated into the capsule core through microencapsulation. Most candidate lipids have at least one ester linkage. In general, these lipids have melting points of 80xc2x0 C.-90xc2x0 C., but some lipids may be liquids at room temperature. Melting of lipid solids may occur over a wide range of temperature, especially when the diluent consists of a mixture of various lipids with different melting points or when those lipids are solids at or just below room temperature (e.g., 20xc2x0-30xc2x0 C.). When the temperature of the surrounding medium rises near or above the melting point of the lipid, i.e., usually during the season and/or the time of the day with high insect activity or mating, the lipid diluent begins to soften or melt, and the active ingredient previously entrapped by the solid diluent is able-to diffuse from the capsule at a higher rate. However, when the temperature falls below the melting point of the lipid and enough to suppress insect activities, the lipid diluent hardens or solidifies and effectively reduces the release of the active pest-control agent by re-entrapping the agent in the hardening or solidifying lipid.
In general, the lipid has a relatively high boiling point, e.g., higher than 200xc2x0 C. at atmospheric pressure and, therefore, hardly evaporates. Accordingly, the potency of the pest-control microcapsule can be effectively prolonged adaptive to the temperature of the surrounding medium. It is appreciated that lipids capable of prolonging functionality of the capsules may melt below room temperature. In this case, the lipid-active ingredient interactions alone in the liquid state prolong release of the active ingredient from the capsules. That is, the pest-control microcapsule includes, in its core, a lipid diluent that is capable of dissolving the active pest-control agent in liquid state to form a homogeneous solution at room temperature (20xc2x0-30xc2x0 C.) By mixing such diluent with the active ingredient, a formulator can effectively entrap the active ingredient within the lipid diluent. When using lipid diluents that are solids at the room temperature, the formulator can customize the melting point of the diluent by manipulating the molecular size and chemical structure of the lipid. For example, the melting point of the lipid including oils, waxes, and fats can vary over a wide range of temperature by manipulating the number of ester linkages as well as the number and characteristics of the short-, medium-, and long-chained fatty acids attached to those ester linkages.
Lipids with aforementioned properties can be obtained from a variety of sources, including minerals, plants, and animals, and may be manufactured by chemical synthesis. Such lipids may be used in their natural form or may be treated by mechanical or chemical processes including filtration, purification, distillation, hydrogenation, and selective crystallization. Examples of those lipids include mineral oil, plant oil, animal oil, animal fat, butterfat oil, butter fat, lard, natural wax, beeswax, insect wax, candellila wax, carnauba, hydrogenated tallow or various plant oils, paraffin wax, and the like. Yet other examples of such lipids include monoglyceride, diglyceride, and triglyceride such as tristearin, tripalmitin, and trilaurin, with or without a free fatty acid.
The sustained-release, pest-control microcapsule of the present invention can be composed of biodegradable and nontoxic compounds. The pest-control microcapsule can include in its core a biopesticide (such as pheromones, pyrethroids, insect growth regulators, and insect attractants or repellents) and an inactive, biodegradable and non-toxic lipid diluent (such as oils, waxes, and fats with ester linkages or cholesterol). However, conventional toxic pest-control agents can also be used along with the inactive, biodegradable, and nontoxic lipid diluent.
The pest-control microcapsule of the present invention can have a density lighter than or comparable to that of water. Generally, lipid diluents are lighter than water and, therefore, microcapsules containing sufficient amount of such lipids float in an aqueous solution on storage. The creamed layer formed by clogged microcapsules may adversely affect the potency and performance characteristics of the microcapsules, unless the capsule slurry is properly formulated. Accordingly, a water-immiscible compound, having at least one ester linkage and having a density greater than that of water, may be added to the lipid diluent in an amount effective to make the microcapsules sink slowly in an aqueous solution or suspending medium. Such water-immiscible compounds can also be added in an amount effective to achieve natural buoyancy of the microcapsule. Examples of such dense lipids include, but are not limited to, triethyl citrate, tributyl citrate, and triacetin.
The pest-control microcapsule of the present invention can also include an antioxidant in the diluent. Addition of an antioxidation agent enhances the oxidative stability of the diluent and, therefore, prolongs potency of the microcapsule as well. Examples of such antioxidation agent include vitamin E oil and synthetic food-grade antioxidants. Sun screen (such as carbon black or other UV absorbers) can also be added in order to provide protection from sun light.
The microcapsules of the present invention can be formed by processes, such as complex coacervation, solvent evaporation, interfacial polymerization (IFP), or in-situ polymerization encapsulation protocols. With IFP protocols, multi-functional acid chloride and isocyanate are employed as shell-forming agents. When the active pest-control agent contains a functionality readily reacting with acid chloride or isocyanate, microcapsules can be formed by complex coacervation, in situ polymerization or solvent evaporation.
In another aspect, this invention features a method of long-term pest control. The steps of the method include mixing an active pest-control agent with an inactive, biodegradable, and nontoxic diluent to the extent effective to entrap the active ingredient by the diluent; microencapsulating the mixture to form a microcapsule with a capsule core and shell; providing resistant mass transfer paths for the active ingredient in the capsule core and the shell; and sustaining the rate of release of the active ingredient through the core and the shell. In particular, the new method can accomplish better entrapping of the active ingredient by dissolving the active ingredient in the diluent in liquid state, and entrapping the active ingredient by the diluent, in which solid diluent is melted at a temperature below 80xc2x0-90xc2x0.
The method also allows the formulator to select a release rate of the active ingredient suitable for pest control and the characteristics of the surrounding medium. For example, the release rate of the active ingredient through the capsule core can be adjusted by manipulating the amount or percentage of the diluent, distribution pattern of the diluent, method of entrapping the active ingredient in the diluent, physical properties of the diluent including its melting point, and temperature of the surrounding medium. Furthermore, the release rate of the active ingredient through the shell can be adjusted by manipulating the composition and homogeneity of the capsule shell, thereby affecting the size, length, density, tortuosity, distribution, and properties of any pores in the shell and diffusivity of the active ingredient through the shell free of pores.
Ease of use or utility of the pest-control microcapsules prepared by any of the above methods can be improved by adding to the diluent a water-immiscible compound heavier than water and having at least one ester linkage in an amount effective to increase resulting density of said microcapsules very close to 1.0. For example, the water-immiscible compound can be added in an amount effective to make resulting microcapsules sink slowly in an aqueous solution or achieve natural buoyancy. Dense microcapsules prepared by these new methods will not float in an aqueous solution and will not form a creamed layer on storage which has detrimental effects on ease of preparing the capsule suspension for field applications.
The potency as well as the shelf life of the pest-control microcapsules prepared by the above methods can also be improved by adding an antioxidation agent to the diluent and/or by adding a sun screen such as carbon black or other UV absorbers.
As used herein, xe2x80x9ccore materialxe2x80x9d of a microcapsule is the material in a microcapsule containing an active pest-control agent to be carried by the microcapsule and to provide effective pest control.
A xe2x80x9cmicrocapsule shellxe2x80x9d is, as used herein, the coating, membrane and/or wall that surrounds the volume material of the microcapsule in which the active ingredient is located. The microcapsule shell provides a physical barrier that separates the contents of the microcapsule from the exterior or surrounding medium in which microcapsules are immersed or placed.
A xe2x80x9cpest-control agentxe2x80x9d is any compound that is toxic to an insect at any stage of its development when ingested or brought into contact with the target insects in some manner (e.g., pyrethroids), any agent that disrupts mating of the target insects (pheromones), any agent that alters the growth and development of insects at some stage of their development (e.g., insect growth regulators), or any agent that acts as an attractant to a xe2x80x9ctrapxe2x80x9d at which the insect is terminated in some manner (e.g., by electric shock, drowning, or physical entrapment as on a sticky surface).
As used herein, a biopesticide is any active pest-control agent that is nontoxic to mammalians. Examples of biopesticides include, but are not limited to, pheromones, pyrethroids, and insect growth regulators.
As used herein, xe2x80x9cdiluentxe2x80x9d means a liquid or solid with a low melting point, for example, below 80 xc2x0 C.-90xc2x0 C., in which the active pest-control agent is soluble either at room temperature or below, at the temperature at which microcapsule formation is carried out (typically at 40xc2x0-60xc2x0 C.), or at the melting temperature of the diluent. Diluents may consist of a single chemical compound or may be a mixture of several components where such diluents are natural products which in their conventional form are composed of multiple components.
As used herein, toxicity generally pertains mainly to mammalians, therefore, plants and fruits treated by the nontoxic pest-control microcapsules are edible.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art related to this invention. Other methods and materials in addition to those specifically described herein can be used in the practice of the present invention. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. The materials, methods, and examples are illustrative only and not intended to be limiting.
Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.
The invention features a sustained-release, long-term pest-control microcapsule which is environmentally friendly and non-toxic, and prolongs its potency by controlling the nature of the diluent in the capsule core in which the pest-control agent is dissolved or dispersed.
In general, a microcapsule includes a capsule core and a capsule shell, both of which can provide resistant paths to the mass transfer of the active pest-control agent contained in the capsule core. Thus, the pest-control microcapsule of the present invention is designed to reduce the rate of release of active ingredient distributed into the surrounding medium, thereby reducing the cost of pest control as well as the potential for environmental pollution by utilizing interactions between the active ingredient and the diluent either in the solid or liquid state.
Diluents used in the microcapsule are selected from the class of materials defined as lipids. Some may form liquid at room temperature and below, while others form solids with low melting point, for example, lower than 80xc2x0 C.-90xc2x0 C. Most lipid diluents include one or more ester linkages where one component of the ester linkage is a fatty acid which is classified as either a short-, medium- or long-chained fatty acid. However, other components without any ester linkage, for example, cholesterol, can also be used as a lipid diluent.
Diluent lipids are often isolated from natural sources (e.g., various plant and animal oils or waxes), are biodegradable, and are non-toxic to all forms of life, thus, generally edible. Examples of diluent lipids include, but are not limited to, plant oils of commerce such as corn oil, soybean oil, canola oil, peanut oil, olive oil, palm oil, coconut oil, cottonseed oil, and sunflower oil. Mixtures of these oils as well as refined or purified oils obtained therefrom can also be used. Such oils refined for specific food or pharmaceutical applications may be classified as oils rich in short-, medium- or long-chained fatty acids. Fats with low melting point produced by varying the degree of hydrogenation of the aforementioned oils or isolated by selective crystallization from various plant oils can also be used. Oils derived from an animal source such as butterfat oil, and low melting point fats from animals such as butterfat and lard can be used as well, although some animal oils may require additional stability control. Natural waxes like bee wax (actually an insect wax produced by bees), carnauba wax (a plant wax), candellila wax (a plant wax), and paraffin wax can also be used. Mixture of these various oils, hydrogenated oils, and waxes derived from various plant or animal source can also be used. A purpose of mixing various oils and waxes is to alter the crystallization temperature of the waxes or hydrogenated oils, thereby altering the temperature at which they soften.
Various aforementioned lipids are relatively pure compounds which may either be isolated from the above mentioned natural plant oil and wax sources or can be prepared by completely synthetic means. Examples include triglycerides such as tristearin, tripalmitin, and trilaurin, as well as triglycerides containing a mixture of one or more different fatty acids. In addition, natural or formulated mixtures of triglycerides, diglycerides, and monoglycerides with or without the additional presence of various free fatty acids can also be used, for such mixtures in reality represent the actual composition of the various plant lipids and animal oils aforementioned.
The formulator can customize the melting point of the diluent by manipulating the size and chemical structure of the lipid. For example, the melting point of the lipid including oils, waxes, and fats can vary over a wide range of temperature by manipulating the number of ester linkages as well as the number and characteristics of the short-, medium-, and long-chained fatty acids attached to those ester linkages.
The diluent is distributed in the core in such a manner that the active pest-control agent is dispersed or dissolved in the diluent and must diffuse through the resistant paths formed by the diluent to reach the capsule shell through which it must subsequently diffuse in order to be released from the capsules. The diluent may operate in several ways. One possible way is that the lipid and pest-control agent have a strong affinity for each other (i.e., mutually miscible) and this affinity reduces the tendency for the pest-control agent to diffuse through the shell. In this case, the AI-lipid mixture may form a liquid at room temperature. Alternatively, the diluent may form a solid-like, matrix-like or mesh-like structure inside the core which effectively entraps the active ingredient inside such matrix and mesh, thereby delaying release thereof. Thus, a formulator can obtain desirable permeability or release rate of the active ingredient by manipulating several factors, such as the amount or percentage of the diluent contained in the capsule core, distribution pattern of the diluent in the core, method of entrapping the active ingredient in the diluent, and other chemical and/or physical properties of the diluent.
The sustained-release, pest-control microcapsule of the present invention may be made of biodegradable and nontoxic compounds. The pest-control microcapsules can include in its core a bio-pesticide such as pheromones, pyrethroids, and insect growth regulators as well as an inactive, biodegradable and nontoxic lipid diluent such as oils, waxes, and fats with ester linkages or cholesterol. However, conventional toxic pest-control agents can also be used along with the inactive, biodegradable, and nontoxic lipid diluent.
Examples of active, biodegradable, and nontoxic pest-control agents include, but are not limited to, biopesticides such as pheromones, pyrethroids, insect growth regulators, and insect attractants or repellents. Conventional toxic pesticidal agents, however, can also be used in conjunction with the aforementioned inactive, bio-degradable, and non-toxic diluents.
The capsule shell separates the core volume material from the surrounding medium, and provides the additional resistant paths, for example, the shell pores and/or other paths, through which the active pest-control agent diffuses into the medium. Thus, permeability or release rate of the active ingredient can be manipulated by controlling at least one of the several factors such as the pore size, length, density, tortuosity, pattern of pore distribution in the shells, and other physical properties of the material constituting the shell. Details as to the formation of such capsule shells will be discussed in greater detail below.
The microcapsules of the present invention may be formed by any of the processes such as complex coacervation, solvent evaporation, interfacial polymerization (IFP), and in-situ polymerization. With IFP, multi-functional acid chloride and isocyanate are used as shell-forming agents. However, when the active pest-control agent contains a functionality which may readily react with acid chloride or isocyanate, microcapsules can be formed by the processes such as complex coacervation, in situ polymerization or solvent evaporation protocols.
Suitability of a given diluent/active pest-control agent for encapsulation can be defined by forming a series of mixtures of active pest-control agents with candidate diluents. When observed visually, they provide a means of assessing whether or not mixtures form a homogeneous solution, and are mutually miscible or compatible. For example, following Examples 1 and 2 summarize some exemplary observations of compatibility of selected diluents and active pest-control agents.